1. Technical Field
The present invention relates in general to an improved disk drive library, and in particular to an improved automated disk drive library.
2. Description of the Related Art
Some present computer systems have the ability to recognize devices that are added to a bus while the computer is operating, that is, without having to reboot the system. “Plug and play” operations allow a computer to configure itself automatically to work with peripherals. The “plug and play” operation allows a computer system to recognize a new device that has been added, but the system typically has to be reset in order to properly initialize the added device with the operating system. “Hot plug” systems and methods were developed as an improvement in this area. In “hot plug” systems and methods, separate reset lines and other features are provided for each peripheral device, such that a device is able to be initialized with the operating system without requiring the entire system to be rebooted (i.e. “hot-pluggable” system).
“Hot-pluggable” devices may be interfaced under various protocols, such as small computer system interface (SCSI), copper fiber or serial storage architecture (SSA), and fiber channel arbitrated loop (FCAL). FIG. 1 shows a SSA example wherein an overall RAID (redundant array of independent disk drives) system 1 with target disk drives 3, that is target drives T0, T1, and T2, are serially linked together to a SSA initiator 6. The SSA RAID system 1 is coupled to and communicates with a central processing unit (CPU) 2 and a host computer 4. The “hot-pluggable” target disk drives 3 are removable from the overall RAID system 1 and thus unlinked from the host computer 4. Typically, a cam mechanism or carrier lever latches the target disk drive 3 to a disk drive drawer. One of the target disk drives 3 is removed from the drawer by unlatching the cam, and the serial link or interface is broken when the target disk drive 3 is physically removed from the drawer.
The problem with the breaking of this link is that the host computer 4 has no way of distinguishing that the target disk drive 3 has been removed over actual problems with the target disk drive 3 or software. Therefore, the host computer 4 assumes that a problem with the target disk drive 3 exists even though the target disk drive 3 has been removed, and various extensive routines and troubleshooting and search algorithms are executed to identify and find the problem despite the fact that the target disk drive 3 has been removed. The computer system 4 attempts to talk to the target disk drive 3 to find a problem, such as data error, power loss, or disk drive removal. In other words, when a target disk drive 3 is removed, the computer system 4 cannot distinguish that the back plane connection for that target disk drive 3 and the link 7 from the backplane connector to SSA initiator 6 have been broken. The host computer 4 assumes that a problem exists and consumes valuable time, power, and computer resources in attempting to identify the problem and to finally find out that the target disk drive 3 has simply been removed. Therefore, the disadvantage and problem with a removable computer interfaced device is that no system or method exists for communicating to the host computer system the fact that such a device has been removed therefrom.
It would therefore be advantageous and desirable to have a system and method of communicating to the SSA initiator and the host computer when a computer interfaced device has been removed from an overall system. It would be advantageous and desirable to provide an automatic enable and disable system and method when a computer interfaced device has been removed from an overall system. It would also be advantageous and desirable to provide a communications system and method to a host computer and to a SSA initiator when an interfaced device has been unlatched and about to be removed from a system, such as when a “hot-pluggable” disk drive has been unlatched and about to be removed from a serial RAID system.
Referring again to FIG. 1, problems also arise when a break in communication or link occurs at any of the target drives 3, such as break 5 at target T0. The serial communication or link has therefore been broken between target T0 and the other serially linked devices, targets T1, T2. As a result, SSA initiator 6 and host computer 4 may no longer be able to access the other serially linked targets T1, T2, such as to access the data stored therein. Therefore, targets T1, T2 typically cannot be accessed until the communication or link problem has been identified and fixed or another access route of the other serially linked target drives are configured. Also, when a break in communication or link occurs, the serial storage architecture is not maintained, and thus the host computer may not be able to recognize the SSA RAID system 1.
It would therefore be advantageous and desirable to have a device for maintaining the serial link between devices when a break in communication or link at one of the devices has occurred. It would also be advantageous and desirable to provide switching of a serial device with a communication or link problem from an inline mode in which the serial device is serially linked to other devices to a by-pass mode in which the serial device is by-passed and the other devices are re-coupled and serially linked together. It would be advantageous and desirable to provide a selfhealing coupler for a serial storage architecture wherein the self-healing coupler bypasses any disk drive or drives in which communication or link has been broken and re-couples and serially links all remaining active disk drives.
In RAID storage subsystems, each drive is loaded in a drive carrier and then mounted in a drawer in the subsystem. The drives are typically provided with a service interface on one end that is accessible only when the drive is not mounted in the carrier. As depicted in FIG. 2, the drive 12 has a maintenance and/or service interface 13 that is usually provided via a conventional RS232 connector. A universal asynchronous receiver/transmitter 9 (UART) provides RS232 capability for downloading debug information, new microcode, etc.
However, when the drives are installed in the RAID drawer, the service interface 13 is not externally accessible due to the presence of the drive carrier 15 (FIG. 3). Carrier 15 has a front bezel 17 that is provided for aesthetic purposes. If a drive were to require external diagnosis or service, the drive must be removed from the drawer. Unfortunately, any volatile failure information contained in the drive at the service interruption would be lost when the drive is removed. In addition, storage device picking mechanisms typically require a significant amount of time to align with, engage, and remove a storage device from a slot. This sequence of events is normally a slower operation than a slot-to-slot transport of a storage device within the library. Finally, the possibility of dropping storage devices while handling them in this manner is always present. Thus, an improved device for interfacing with and handling storage devices in an automated library is needed that is externally accessible.
In one type of RAID, the disk drives receive operational and data signals from the host computer through a fiber optic backplane. Typically, a single fiber optic cable extends along the backplane and is distributed to a series of fiber optic junctions. The fiber optic junctions must be readily equipped to detach from one disk drive and reattached to another since some of the drives will inevitably fail, and some applications require the drives to be frequently replaced. When a drive is removed from a junction, the junction must relay the optical transmission downstream with minimal losses. Unfortunately, each prior art, fiber optic junction typically causes about 6 dB in losses in the transmission of the signal. Thus, although prior art designs are workable, a more efficient optical junction for disk drive fiber optic cable backplanes is needed.
The power requirements of the disk drives in a RAID are typically provided through a hard-wired connector interface with the backplane. Although current power interface hardware is acceptable, an improved apparatus and method for powering to arrays of independent disk drives is desirable.
Finally, each disk drive carrier typically utilizes a cam mechanism in order to latch itself and the disk drive into a drawer. Unfortunately, the lever that operates the cam must be manually actuated to install or remove the drive carrier from the drawer. Thus, an improved mechanism for installing and removing drive carriers that alleviates the need for manual intervention is needed. Moreover, an automated library that satisfies each of the previously mentioned needs in the prior art would be desirable.